1. Field of the Invention
The present invention relates to an image bearing member-protecting agent which is supplied to an image bearing member contained in image forming apparatuses such as copiers, facsimiles and printers, a protecting agent-supplying device which supplies the image bearing member-protecting agent to an image bearing member, a process cartridge or an image forming apparatus containing the protecting agent-supplying device, and an image forming method using the image forming apparatus.
2. Description of the Related Art
In image forming apparatuses having an image bearing member (e.g., a photoconductor made of, for example, a photoconductive compound), the image bearing member is rotated and subjected sequentially to, for example, a charging step, an exposing step, a developing step, a transfer step and a fixing step for image formation.
In the charging step, the surface of the image bearing member is charged with a charging member such as a charging roller. In the exposing step, a latent electrostatic image is formed on the surface of the image bearing member whose surface has been charged in the charging step. In the developing step, charged tone particles are made to adhere to the latent electrostatic image on the image bearing member surface, to thereby form a visible image. In the transfer step, the visible image is transferred from the image bearing member onto a recording medium (transfer medium) such as paper. In the fixing step, the visible image transferred onto the recording medium is fixed thereon with, for example, heat, pressure or gaseous solvent. Through these steps, an output image is formed on the recording medium.
The developing method in the developing step is roughly classified, depending on the method of charging toner particles, into a two-component developing method and a one-component developing method. In the two-component developing method, toner particles are stirred/mixed with carrier particles and are frictionally charged. In the one-component developing method, toner particles are charged with no use of carrier particles. The one-component developing method is further classified into a magnetic one-component developing method and a non-magnetic one-component developing method, depending on whether or not the developer bearing member (for bearing toner particles) retains toner particles by a magnetic force.
Of these developing methods, the two-component developing method is often employed in, for example, copiers required for high-speed processing and developing reproducibility, and complex machines employing such copiers, in terms of charging stability of the toner particles, charge rising property, long-term stability of image quality, and other requirements. Meanwhile, the one-component developing method is often employed in the compact printers and facsimiles.
In recent years, color images are generally formed, and thus, demand has increasingly arisen for high image quality and stability of image quality. These requirements are intended to be met not by improving the developing method, but by decreasing the average particle diameter of toner particles and using more spherical toner particles. For example, toners produced with the polymerization method are seen on the market. These toners have advantageous features in that they have less angular portions and a uniform average particle diameter, as compared with toners produced with the pulverizing method. In addition, the polymerized toners contribute to not only improvement of image quality but also saving of production energy.
The image bearing member having undergone the transfer step has, on the surface thereof, residual toner components which have not been transferred onto the transfer medium. When charged again in the charging step in this state, the image bearing member is not uniformly charged in many cases. Thus, in general, a cleaning step is additionally provided after the transfer step and before the next charging step. In the cleaning step, the toner components and other foreign matters (e.g., paper dust) remaining on the image bearing member are removed with a cleaning member such as a cleaning blade, and the image bearing member surface is sufficiently cleaned before the charging step.
The recent toner particles have a smaller average particle diameter and a more spherical shape as described above. Such toner particles are more difficult to remove in the cleaning step. In one countermeasure against this, the cleaning member is pressed against the image bearing member surface at larger pressures.
As described above, the image bearing member receives various physical or electrical stresses in the above steps, and the state thereof changes over time, especially after long-term use. For example, the image bearing member receives considerable electrical stress in the contact charging method or close-contact charging method (which involves a discharging phenomenon in the vicinity of the image bearing member surface), since, in these charging methods, many active species or reaction products are formed on the image bearing member surface, and active species or reaction products formed in air within the discharging region adsorb on the image bearing member surface in a large amount. Also, it is known that, when the alternating voltage is employed in the charging step, the stress caused by the application of the voltage abrades the image bearing member. In addition, as has been known, the stress caused by the friction in the cleaning step abrades and scratches the image bearing member, and also abrades the cleaning member. Thus, conventionally, many researchers have proposed methods of supplying a lubricant or lubricating ingredients and of forming a film on the image bearing member surface from the lubricant or lubricating ingredients, in order to reduce, the friction force between the image bearing member and the cleaning member.
For example, some patent literatures disclose techniques of forming a lubricant film on the surface of a photoconductor (image bearing member) by supplying a lubricant (image bearing member-protecting agent) onto the photoconductor surface to elongate the service lives of the photoconductor and the cleaning member (see, for example, Japanese Patent Application Publication (JP-B) No. 51-22380, and Japanese Patent Application Laid-Open (JP-A) Nos. 2001-305907, 2007-293240, 2007-65100 and 2006-350240). Using the above techniques, the stress applied to the image bearing member in, for example, the charging step can be easily reduced.
Meanwhile, for the lubricant, there are known lubricants mainly containing a fatty acid zinc salt (see, for example, JP-B No. 51-22380 and JP-A Nos. 2001-305907, 2007-293240 and 2007-65100) and lubricants containing a fatty acid metal salt and an inorganic lubricant (see, for example, JP-A No. 2006-350240). The latter lubricants decrease in lubricity to a less extent than in the former lubricants, even when receiving the stress due to discharge in the charging step. In addition, even when the recent small/spherical toner particles are used, the latter lubricants are suitable for suppressing or preventing the cleaning member from being abraded, and suppressing or preventing the toner particles from running through the cleaning member to stain the charging member or adversely affect the formed image. Furthermore, they are suitable for suppressing or preventing the lubricating ingredients as well as toner particles from running through the cleaning member to stain the charging member.
In recent years, cleaning performance for toner has been remarkably improved in the cleaning steps, and the recent small and highly spherical toner particles are cleaned effectively. Such improved cleaning performance prevents toner particles from running through the cleaning step, which prevents the photoconductor and cleaning member from being abraded (i.e., their service lives from being shortened) and the charging member from being stained (i.e., the service life from being shortened). In view of this, the supply of the latter lubricant onto the photoconductor is advantageous in elongating the service lives of the photoconductor, the cleaning member (in the cleaning step) and the charging member.
In one known configuration in which a lubricant is supplied to the photoconductor surface, a brush is rubbed against a solid bar lubricant so that the lubricant is scraped off and supplied to the photoconductor (see, for example, JP-A Nos. 2001-305907, 2007-293240, 2007-65100 and 2006-350240).
In another known configuration in which a lubricant is supplied to the photoconductor surface, a solid lubricant is elastically brought into contact with a brush to maintain constant, for a long period of time, the amount of the lubricant supplied to the photoconductor (see, for example, JP-A Nos. 2001-305907, 2007-293240 and 2007-65100). Furthermore, there have been proposed various configurations for stabilizing, for a long period of time, the amount of the lubricant supplied to the photoconductor (see, for example, JP-A Nos. 2007-293240 and 2007-65100).
Meanwhile, compression molding and melt molding are known as methods of solidifying a lubricant so as to have a bar shape (see, for example, JP-A No. 2006-350240). The lubricant obtained through melt molding is harder than that obtained through compression molding. Thus, the amount of the former lubricant supplied to the photoconductor is problematically decreased. In particular, as revealed from the studies of the present inventors, a lubricant formed by mixing an inorganic lubricant with a fatty acid metal salt is likely to raise this problem. This is probably because the inorganic lubricant serves as a filler.
Therefore, in order to ensure the amount of a lubricant supplied to a photoconductor and to elongate service lives of a photoconductor, a cleaning member and a charging member, it is desired that compression molding is employed to mold/solidify a lubricant containing a fatty acid metal salt and an inorganic lubricant.
The lubricant molded/solidified through compression molding is soft. When such a soft lubricant is used in conventional configurations which stabilize for a long period of time the amount of a lubricant supplied to a photoconductor (see, for example, JP-A Nos. 2007-293240 and 2007-65100), a brush is rubbed ununiformly against the lubricant (protecting agent) to mainly consume the protecting agent at one side only (ununiform scraping). As a result, the amount of the lubricant supplied is not sufficiently consistent for a long period of time.